Known art using deformation characteristics of crystal-construction of piezo-electric elements while being subjected to electrical voltages includes U.S. Pat. No. 5,640,065 entitled "Ultrasonic Motor and Method of Driving the Same" and awarded to Abe et al. on Jun. 17, 1997, where the patent discloses an ultrasonic motor comprising a piezo-electric element functioning as a driving source, a rectangular-parallelepipedic elastic body coupled to the piezo-electric element; and a driving circuit for generating a driving signal having attenuation characteristics in a vibration attenuation period of the elastic body, thereby generating an extending/contracting vibration along a longitudinal direction of the elastic body and a bending vibration propagating in the longitudinal direction of the elastic body. The motor is implemented in micro-machining operation and is capable of enhancing positioning precision of a driven object.
Furthermore, prior art using deformation of a piezo-electric element while being subjected to voltages so as to generate driven motions includes an article entitled "Energy Saving Effect of Micro-Lathe" published in "Microengineering and the Global Environment" in November 1996 by Tokio Kitahara, where the article discloses a micro-lathe comprising a mainshaft unit, an X-Y driving unit, and a tool rest. The micro-lathe measures 32.0 mm in length, 25.0 mm in depth, and 30.5 mm in height, and weighs 100 g. The micro-lathe is implemented in cutting miniature parts of several millimeters or less in diameter. The mainshaft unit that consists of a mainshaft and micro-motor is fixed on the X-Y driving unit and is movable in both X- and Y- directions. The lower part of the X-Y driving unit serves as a bed. The tool rest is fixed on one end of the bed. Workpiece is retained in a holder which is integrally constructed with the mainshaft. When cutting, the workpiece is moved to the stationary cutting tool. Rotation of micro-motor transmits to the mainshaft via a rubber belt. The mainshaft speed is variable in approximately 8,000 to 15,000 rpm range. As illustrated in FIG. 8, the X-Y driving unit which comprises two linear driving units 70, 80, can drive the mainshaft unit in the range of 4 mm in both X- and Y- directions. Each linear driving unit 70, 80 comprises a slider 71, 81 and a V-shaped guide device 90 on opposing sides of the linear driving unit 70, 80. A guide 91 located on one side is stationary and another guide 92 is urged by a spring 93 that subjects a lateral thrust. The sliders 71, 81 include piezo-electric elements 72, 82. In operation, voltages are applied to the piezo-electric element 72 within the first linear driving unit 70 to cause lateral expansion. Voltages are then applied to the piezo-electric element 82 within the second linear driving unit 80 to cause longitudinal expansion of the slider 81. Because one end of the slider 81 is blocked by the stationary slider 71 while expansion, the slider 81 may only move and expand forward at a minute distance from the other end. Voltages applied to the first linear driving unit 70 is then removed to cause contraction of the piezo-electric element 72 such that the slider 71 is freely movable on the guide device 90 and the first driving unit 70 is driven to move forward. Voltages applied to the piezo-electric element 82 within the second linear driving unit 80 is then removed to cause contraction of the piezo-electric element 82. However, the sliders 71, 81 are maintained at the aforesaid position due to resilience of the spring 93. The fore-described operations are then repeated to cause the piezo-electric elements 72, 82 to be under control of voltages of accelerated frequency so as to generate expeditious changes of expansion or contraction. The first and second linear driving units 70, 80 thus move forward in minute increments. The first and second linear driving units 70, 80 moving direction is reversed when phase-difference of the voltages being applied to the piezo-electric elements 72, 82.
However, the slider 81 of the second linear driving unit 80 of the aforesaid micro-lathe is only capable of expansion or contraction motions in longitudinal direction without lateral expansion to urge against a guide device 90. When the slider 81 expands as a result of expansion of the piezo-electric element 82, removal of voltages causes the piezo-electric element 72 of the slider 71, thereby subjecting the slider 81 to move a minute distance forward. When the slider 81 moves a distance forward, voltages applied to the piezo-electric element 82 are removed to repeat the aforesaid operation. However, at this moment, contraction of the slider 81 tends to move backwards. Such backward tendency is reduced because the spring 92 urges against the sliders 71, 81, but not completely offset.